1. Field of the Invention
The present invention relates to a sheet feeder unit mounted in an image forming apparatus or the like having a sheet transport mechanism.
2. Description of the Prior Art
An image forming apparatus such as a copying machine is provided with a sheet transport mechanism for transporting copy paper. The sheet transport mechanism usually transports copy paper fed from a relatively compact paper cassette holding sheets of copy paper and mounted in the image forming apparatus.
A compact paper cassette usually mounted in a copying machine can only hold a limited number of sheets and therefore may run out of sheets when a large number of copies are to be made successively. In view of this problem, a large capacity sheet feeder unit capable of holding a large quantity of copy paper and having a mechanism to feed copy paper to the sheet transport mechanism is used instead of a conventional compact paper cassette. Use of such a sheet feeder unit permits continuous copying in large volumes.
Such a sheet feeder unit is detachably mounted in the copying machine, and the sheets contained therein are fed to the sheet transport mechanism by means of a paper feed roller driven by a driving means separately provided from that for the sheet transport mechanism of the copying machine. In recent years, in offices where large volumes of documents are handled, more than one copying machine has come to be installed, and it is sometimes the case that one sheet feeder unit is used with different copying machines. However, the sheet transporting speed of the sheet transport mechanism is not exactly the same between these different copying machines. Therefore, when making a large number of copies on one copying machine using such a sheet feeder unit, there is a possibility that a sheet fed from the sheet feeder unit into the sheet transport mechanism may overlap the preceding sheet being transported by the sheet transport mechanism, thereby causing jamming of paper. Particularly in the case of copying machines of different makers, the sheet transporting speed of the sheet transport mechanism may be greatly different between such machines, which, when one sheet feeder unit is shared between them, results in more chances of paper jamming.